Former Prime Minister Gordon Brown has called for air and satellite support in the hunt for almost 300 abducted Nigerian schoolgirls to be extended to neighbouring African states.

Mr Brown welcomed an offer from teachers in Cameroon, Chad and Niger to keep a watch out for the girls, but said surveillance from the skies will be needed.

He held talks with Nigerian president Goodluck Jonathan in his role as United Nations Special Envoy for Global Education, and assured him of the support being offered by world community in the hunt for the 276 missing girls. He said: "I've been advocating action for three weeks and it's now time to go beyond the words of comfort. We have to extend the search for these girls now beyond Nigeria... into Cameroon, into Chad, into Niger. The air support and surveillance we need and the satellite coverage has now got to go into a number of other states to find the girls.

"My message to the families is, we will now do everything in our power, even though it's late, we will do everything in our power to try to locate these girls."

Islamist militants from the Boko Haram group have warned that they will sell the girls into slavery.